Steam is used as a source of power in a variety of applications, including steam generators and steam turbines. Steam is used for heating, sterilizing, humidifying, and evaporating in several sectors such as oil refining, nuclear power plants, and food plants, as well as pharmaceutical manufacturing plants. In certain applications it is critical to know the quality of the steam used, that is, the dryness and non-condensable gases content of the steam, since any deviation in steam quality for these critical applications would create undesirable consequences. Bad steam quality is not suitable for sterilizing, can erode turbine blades, and can create water hammer in piping.
Until now such measurements required human intervention for a manual sampling of the steam. This manual process is not fully reliable, is time consuming and is not safe (for example, risk of burning while installing the connections for the sampling, or while taking the samples).
Steam dryness may be determined in several ways, including by using a throttling calorimeter. Examples of known steam quality measurement systems and methods are disclosed in U.S. Pat. No. 4,833,688, issued to Smith, and U.S. Pat. No. 5,327,772, issued to Fredricks.
For the throttling calorimeter to provide useful steam quality data, the steam sample must be in a single phase (i.e., gaseous). This may be achieved by ensuring that the steam is in a superheated state. For the majority of industrial steam systems that have working pressures above 10 bar this is easily achieved by reducing the pressure. Unfortunately, this method has a limited working range for low pressure systems, for example, those operating at 3 bar gauge (e.g., 97% dryness). This method is therefore unsuitable for pharmaceutical industry steam applications that utilize steam at a relatively low pressure and require measurement of dryness across a range of 90 to 100%.
It is also desirable to measure and monitor the content of non-condensable gases (i.e., air) in the steam.
It is also desirable to measure whether the steam is in a “superheated” condition.